Functional genomics combines two approaches: working from genes to biological functions and working from biological functions to genes. In the last several years, we have developed a series of methods to study gene function in the nematode C. elegans. These include effective reporter-based technology to follow gene expression in live animals, methods for ectopic or overexpression in specific somatic tissues, and a novel RNA-mediated genetic interference procedure for studying loss-of-function effects. Tools developed in this lab have combined with numerous advances elsewhere and with ongoing genome sequencing efforts in facilitating the emergence of C. elegans as a pre-eminent model for both forward and reverse approaches to gene function. Making use of these tools, we have begun to analyze genetic contributions to patterning of two mesodermal tissues: germline and muscle. This work has resulted in identification and characterization of a number of genes regulating acquisition and retention of mesodermal fates. Several of these genes are counterparts of human genes known to produce craniofacial and other mesodermal abnormalities in individuals with mutant copies. This species conservation indicates a relevance to human health. In the long term we hope that our research will yield direct medical applications both by providing knowledge of underlying developmental pathways and by providing functional assay systems which can assist in developing diagnosis and treatment procedures. We propose to continue development of molecular-genetic technology for C. elegans. Major goals include techniques for global and tissue-specific gene knockout, techniques to engineer ectopic expression in limited temporal and spatial patterns, and the extension of expression technology from the soma (where techniques have become quite effective) to the germline (where many straightforward manipulations have so far been difficult). Concurrently, we propose further analysis of fate specification and differentiation in mesodermal tissue. Future plans include (1) Additional characterization of genes that we already know to function in this process (detailed analysis of expression patterns and loss-of-function phenotypes to illuminate the roles of each component in the overall developmental pathway) and (2) Forward and reverse genetic screens to identify remaining components in mesodermal patterning. As we uncover individual genes that are involved in mesodermal specification, we will work toward defining interactions among the corresponding gene products and understanding the regulatory networks that lead to the production of a defined spatial lineage pattern.